Fujiwhara and Northeast Hurricanes

On Saturday I attended the Tri-State Weather Conference out at WestConn in Danbury. Dr. Bob Hart, a North Branford native who’s a professor at Florida State University, gave a superb talk on the 1938 hurricane.

We know a lot about the 1938 hurricane. It’s been looked at and researched quite a bit. We are now able to get a new look at the storm thanks to the 20th Century Reanalysis which uses historical surface observations to recreate a “six-hourly, four-dimensional global atmospheric dataset spanning 1871 to 2010 to place current atmospheric circulation patterns into a historical perspective.”

Now we’re able to get a better idea what the synoptic pattern looked like during at after the 1938 storm. Here’s a look at the sea level pressure and 500 mb ensemble mean height reanalysis for12z 9/21/1938.

No big surprises here with a deep, anomalous 500mb cut off low essentially capturing the 1938 hurricane and rocketing it north. A large portion of Dr. Hart’s presentation was about 38’s unusual (and dangerous) extra tropical transition to warm seclusion and associated problems with predictability.

He also talked about the 1893 hurricane which brought a devastating storm surge to New York City. The 1893 storm took an unusual path. Instead of losing longitude as it moved north of the Carolinas is continued due north to New York City.

1893 Hurricanes #4 and #6

While 1893 Hurricane #4 barrelled toward New York City there was another hurricane nipping on its heels. The best track data shows 1893 hurricanes #4 and #6 on very different paths. On August 24 at 00z hurricane #4 was just east of Norfolk, VA while hurricane #6 was just north of Puerto Rico as caetgory 2 and 3 storms, respectively. The 20th century reanalysis data shows an impressive parade of Atlantic hurricanes but a relatively unimpressive 500 mb trough over the Great Lakes (though there is strong ridging over the North Atlantic).

So what lead the 1893 hurricane to smash right into New York City and not head out to sea? Dr. Hart argues the Fujiwhara effect kept Hurricane #4 close to the coast as the interaction between the 2 powerful cyclones resulted in Fujiwhara behavior. Wild stuff, right? While Fujiwhara can result in beautiful interactions in the west Pacific it is more unusual (but certainly not unheard of) in the Atlantic. While these 2 hurricanes didn’t make a complete loop Fujiwhara appears to have influenced the hurricanes track.

Connie and Diane in 1955 lead to one of the state’s worst natural disasters on record (see here).

While I had always noted their unusual track burps with Connie’s sharp right south of Hatteras and Diane’s sharp left southeast of Bermuda I had never really given it much thought. Hart cited this as an example of Fujiwhara interaction between the 2 cyclones.

While Fujiwhara is fun to say it can lead to a model meltdown. One of the most sobering parts of Dr. Hart’s talk was about the breakdown in predictability of a tropical cyclone’s track when Fujiwhara interaction is involved. Using the 20th century reanalysis as an initial condition the model Dr. Hart ran (I believe it was a WRF ensemble) showed exceptional spread and run-to-run variability in the 1893 case. The potential for dramatic track errors in a short period of time is alarming – particularly for the kind of storm that brought a 25 foot storm surge to New York City.

Getting a hurricane into New York or southern New England is unusual. While many follow a rather predictable pattern there are exceptions with highly anomalous flow regimes or Fujiwhara interactions that, according to Dr. Hart, can lead to breakdowns in predictability. Certainly a sobering thought from an emergency management and operational meteorology perspective.

3 thoughts on “Fujiwhara and Northeast Hurricanes”

Hi Ryan, I’m a little puzzled (from my layman’s perspective) that Diane’s sharp turn westward occurred when Connie was hundreds of miles away. Also what isn’t clear is the position of both storms respectively when they exhibited the Fujiwhara effect. Did they both make their turns at the same time; i.e. when Diane was near Bermuda and Connie south of Cape Hatteras? If that’s the case why wouldn’t they exhibit any rotation around each other at all prior to that time?

By the way, love your blog and my wife (Stef who worked with you at Mickey Finn’s) says ‘hi’,

Hey Ron… the Fujiwhara Effect can occur when the storms are very far apart. Their circulations are extremely broad – well beyond the storm’s center. And they made their turns near the same time… probably not at the same time. Check out the Wikipedia page on Fujiwhara it may answer some questions. A Google search will yield some cool videos too. While Fujiwhara influenced their track it was temporary. As soon as Connie got caught up in the jet stream that interaction became much more dominant and steered the storm away.